Warm and Buttery: Melt Speeds Greenland's Ice Flow

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Greenland's massive ice sheet is accelerating its slide toward
the ocean because bigger surface melts in recent years are
softening the interior of the ice like a stick of butter, a new
study finds.

For more than a decade, scientists have reported rapid melting
and shrinking at many of
Greenland's outlet glaciers, which snake into the ocean.
Studies suggest warmer ocean water and rising atmospheric
temperatures contribute to the melting ice. The new study finds
the interior ice sheet also speeded up its flow to the sea in the
past decade, but for a different reason. The ice sheet is
changing from within.

"It's not just melt at the edge that's affecting
how Greenland is changing," said Thomas Phillips, lead study
author and a glaciologist at the Cooperative Institute for
Research in Environmental Sciences (CIRES) at the University of
Colorado Boulder. "This is a totally different mechanism. It
comes from within the ice, and that's why we think this is such
an important finding. This ice is changing its behavior as a
whole, not just at the edges."

Like butter

Surface meltwater ponds and lakes form on top of Greenland's ice
sheet and glaciers every summer. The water pressure can fracture
the surface, creating a vertical drainpipe that carries the
surface meltwater into the ice, even down to the rock at its
base. The liquid lubricates the ice sheet, helping it slide more
easily.

But the researchers also think the meltwater is softening the
solid ice, making it deform like a stick of butter. The water
transports heat into the chilly interior ice, according to
computer modeling by the research team. The softer ice also flows
more quickly, the modeling suggests. [ Image
Gallery: Greenland's Melting Glaciers ]

The study focused on Sermeq Avannarleq Glacier in southwest
Greenland. Located about 40 to 60 miles (65 to 95 kilometers)
from the coast, the glacier is flowing about 1.5 times faster
than it was 10 years ago. In 2000, the inland segment was flowing
about 130 feet (40 meters) per year; in 2007-08, that speed was
closer to 200 feet (60 m) per year.

Additional work by the team hints that other regions of
Greenland's ice sheet are also accelerating because of surface
melting, Phillips said. "There are indications that this is going
on in large areas, and we're probably going to see more of this
happening in the future," Phillips told LiveScience.

Glaciers slow, ice sheet speeds up?

The new findings also suggest Greenland's future melt may be more
extensive than recent studies conclude. Some scientists think the
rapid shrinking of its outlet glaciers may slow in coming
decades. But even if the outlet glaciers slow down, the interior
ice sheet could continue to speed up, spurred on by the extensive
surface melts of recent years, Phillips said.

In 2012, nearly the entire surface veneer of Greenland's ice
sheet melted, the
biggest surface melt since record-keeping started 30 years
ago.

"When we started studying this in 2005, we didn't expect to see
all of Greenland melt within our lifetime, and seven years later
it happened. It's changing very, very rapidly up there," Phillips
said.

The findings were published May 6 in the Journal of Geophysical
Research: Earth Surface.